21 
Table IX. — Showing relative rate of Jlocadation by acids and their salts. 
Salt or acid. 
H,S04..-. 
Al2(S04)3. 
CaS04.... 
MgS04.... 
K^04.... 
NasS04... 
(NH4)sS0 
HCl 
CaClj 
MgCl, 
KCl 
Time required for 
flocculation. 
T^normal 
solution. 
Hours. 
1 
1 
9 
4 
105 
120 
147 
1 
1 
3 
165 
^J^normal 
solution. 
Hours. 
Salt or acid. 
NaCl 
NH4CI 
HNO3 
Ca(N0,)2.. 
Mk(N03)2.. 
KNO3 
NaNOs.... 
NH4N03... 
H3PO4 
CaHP04..- 
CH3COOH 
Time required for 
flocculation. 
T^normal 
solution. 
Hours. 
120 
103 
1 
1 
2J 
48 
150 
72 
li 
li 
15 
^i^normal 
solution. 
Hours. 
2 
72 
144 
192 
I 
These results agree to a certain extent with the findings of other 
investigators. They indicate a relationship between the valency of 
the salt and its flocculating power. The most active salt is aluminum 
sulphate, a trivalent salt and one which is highly hydrolyzed. The 
divalent calcium and magnesium salts of nitric, hydrochloric, and 
sulphuric acids are next, while the monovalent salts of sodium, 
potassium, and ammonium are least active. The acids are stronger 
than any of their divalent salts but the trivalent salt, aluminum sul- 
phate, is stronger than any of the acids. Nitric acid is the strongest, 
hydrochloric second, and sulphuric third. Likewise the nitrates and 
chlorids are stronger than the sulphates. This indicates that the 
degree of flocculation is related both to the acidity and the basicity. 
Phosphoric and acetic acids cause much less flocculation than the 
other acids. 
Thus far no investigator has been able to satisfactorily explain 
this phenomenon, although various theories have been advanced/ 
The explanation is probably to be found within the realm of collofd 
chemistry. Hall and Morrison suggest that some physicist must first 
arrive at a satisfactory explanation of Brownian motion. They* 
have recently suggested the possible presence of free alkali derived 
from the partial hydrolysis of the suspended material and that floc- 
culation ensues when these are neutralized. Hilgard assumed a chem- 
ical hydration of the fine particles of clay when in suspension which 
when lime was added became dehydrated, causing a flocculation of 
the soil particles. 
Regarding the composition of soil colloids Uttle is known. While 
many authors have assumed them to be inorganic it is probable that 
being characteristic of the states of matter from which they are 
formed and not of any particular substance, they may be partly 
organic. Free^ suggests that organic colloids may coat the soil 
particles with thin films. 
1 Jour. Agr. Sci., 2 (1907), No. 3, pp. 244-256. 
a Jour. Franklin Inst., 169 (1910), No. 6, pp. 421-438; 170 (1910), No. 1, pp. 46-57. 
